The gonadotropin stimulation hypothesis is a leading idea in the etiology of ovarian cancer explaining the association of cancer risk with the number of ovulatory cycles. However, gonadotropins have only unremarkable effects on the growth of ovarian surface epithelial cells in culture. Thus, a convincing mechanism for the ovarian carcinogenic activity of gonadotropins is lacking. Recently, we found that pre-neoplastic ovarian surface epithelia that are located immediately adjacent to morphologically neoplastic lesions often lack basement membranes and have proposed that the loss of basement membrane is an early step in ovarian tumorigenicity. Thus, we hypothesize a mechanism for the carcinogenic effect of gonadotropins, that the hormones stimulate the loss of basement membranes similar to pre-ovulatory events. As a result, the frequent placement of the ovarian surface epithelium in such a basement membrane-less, pre-neoplastic stage by repeated gonadotropin stimulation increases the frequency for tumor prone cells to transform Gonadotropins induce Cox-2 in both granulosa and surface epithelial cells to mediate ovulation, and the loss of basement membrane and other ovulatory events can be blocked by inhibition of the Cox enzymes. The W or Wv mice are predisposed to tubular adenoma formation from the ovarian surface epithelium. The cause of ovarian neoplasm is thought to be the elevated serum gonadotropins in these spontaneously mutant mice. Another genetically engineered mutant mouse, the Disabled-2 (Dab2) heterozygous knockout model, is also predisposed to the development of ovarian surface epithelial dysplasia and papillomatosis, the pre-malignant lesions of ovarian cancer. We speculate that the combination of Wv/Wv and Dab2 () genotypes will augment the predisposition to ovarian neoplasm. We will test if the inhibition of Cox enzymes reduces the gonadotropin stimulated basement membrane loss, and inhibits or reduces the predisposition of the Wv/Wv, Dab2 () mice to develop ovarian tumors. To investigate the mechanisms, we will also examine the effects of gonadotropin stimulation on the expression of Cox-2, collagen IV, laminin, and MMPs in ovarian surface epithelial cells in culture. These studies will help to understand the etiology of ovarian cancer related to gonadotropins, and provide a mechanism(s) for the chemopreventive activity of Cox-2 inhibitors.